1. Field of the Invention
The present invention relates to a liquid crystal display device that drives a liquid crystal layer on a substrate surface using a horizontal electric field.
2. Description of the Background Art
In a general liquid crystal display device, electrodes are respectively provided to each of a pair of substrates that are disposed facing each other and which sandwich a liquid crystal layer, and brightness control of display area is achieved by producing an electric field in a direction orthogonal to the substrate surface using these electrodes, thereby changing the orientation of the liquid crystal layer. In such a liquid crystal display device, the liquid crystal molecules of the liquid crystal layer are oriented at an incline with respect to the substrate surface when an electric field is applied, causing the inclined direction to be biased in one direction and, in turn, visual angle dependency to occur in the brightness control of display area.
In order to eliminate such a disadvantage, liquid crystal display devices capable of achieving favorable viewing angle dependency have been disclosed in Japanese Unexamined Patent Application Publication No. 56-91277 (hereinafter referred to as “Patent Document 1”) and Japanese Unexamined Patent Application Publication No. 07-72491 (hereinafter referred to as “Patent Document 2”), for example. The liquid crystal display devices disclosed in Patent Document 1 and Patent Document 2 provide a display electrode and a common electrode on a surface of one of a pair of substrates, respectively, that are disposed facing each other and which sandwich a liquid crystal layer, and achieve brightness control of display area by producing an electric field in the substantially horizontal direction on the substrate surface using the area between both electrodes, thereby changing the orientation of the liquid crystal layer. With such a liquid crystal display device, viewing angle dependency is not likely to occur in the brightness control of display area since the liquid crystal molecules of the liquid crystal layer change orientation on the substrate surface while remaining in a horizontal state when an electric field is applied, making it possible to achieve favorable viewing angle dependency. Such a liquid crystal display device is called an in-plane switching (IPS) mode liquid crystal display device. The liquid crystal display device disclosed in Patent Document 1 is an active matrix driven type wherein active elements such as a thin film transistor are provided to each crossing part of a display electrode and a common electrode to switch each pixel. On the other hand, the liquid crystal display device disclosed in Patent Document 2 is a simple passive matrix driven type that does not use active elements such as described above.
However, while both IPS mode liquid crystal display devices of the preceding examples assume that a plurality of pixels is disposed in a dot-matrix pattern to display an image, they do not propose a structure suitable for a segment display-type liquid crystal display device comprising an arbitrary display part shape. Specifically, in the IPS mode liquid crystal display devices of the preceding examples, a crossing section always exists in the planar view of the display electrodes and counter electrodes or the lead wirings connected thereto, and the insulation of this crossing section is achieved by interposing an insulating film. The provision of such an insulating film causes an increase in the number of processes at the time of liquid crystal display device manufacture. Hence, according to the liquid crystal display device disclosed in Patent Document 1, the insulating film of the crossing section described above can be formed in conjunction with the formation of a passivation film that is provided to construct the active elements, making insulating film formation less likely to cause an increase in the number of manufacturing processes.
Nevertheless, active elements are generally not provided in the segment display-type liquid crystal display device, resulting in concern that the number of manufacturing processes will increase in a case where the decision is made to provide an insulating film at a crossing section such as described above. On the other hand, while to ensure that a crossing section is not provided requires that all lead wirings respectively corresponding to the display electrode and counter electrode be disposed on the same surface, the amount of lead wirings increases with an increase in the number of display parts, making it difficult to dispose each electrode and lead wiring on the same surface without providing a crossing section.
It is therefore an object of a specific mode of the present invention to provide an IPS mode liquid crystal display device in which it is easy to dispose each electrode and lead wiring on the same surface, and which is suitable for a segment display type.